Re: [swift-evolution] [Review] SE-0174: Change `filter` to return an associated type

[T.J. Usiyan via swift-evolution]

+1

There are many things that I would like more but this is a reasonable
compromise.



On Mon, May 1, 2017 at 8:02 PM, Nevin Brackett-Rozinsky via swift-evolution
 wrote:

> Another possibility is to make “map” generic on the return type, something
> like:
>
> extension Collection {
> func map (transform: (Iterator.Element)
> throws -> T.Iterator.Element) rethrows -> T {
> var result = T()
> for e in self { try result.append(transform(e)) }
> return result
> }
> }
>
> That way the user can choose what type they want. And since there is also
> a more-specific implementation returning an Array, that is what you’ll get
> if context does not constrain the type, so existing code will still work
> the same.
>
> We could do the same for “filter”, in which case the current proposal
> would just change what the default type is. So…what I’m talking about here
> would be purely additive and can happen later.
>
> In any case, I do like the idea being proposed in SE–0174. If I have a
> collection and I filter it down, it makes sense to still be the same kind
> of collection. So, +1 from me.
>
> Nevin
>
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Re: [swift-evolution] [Review] SE-0174: Change `filter` to return an associated type

[Nevin Brackett-Rozinsky via swift-evolution]

Another possibility is to make “map” generic on the return type, something
like:

extension Collection {
func map (transform: (Iterator.Element)
throws -> T.Iterator.Element) rethrows -> T {
var result = T()
for e in self { try result.append(transform(e)) }
return result
}
}

That way the user can choose what type they want. And since there is also a
more-specific implementation returning an Array, that is what you’ll get if
context does not constrain the type, so existing code will still work the
same.

We could do the same for “filter”, in which case the current proposal would
just change what the default type is. So…what I’m talking about here would
be purely additive and can happen later.

In any case, I do like the idea being proposed in SE–0174. If I have a
collection and I filter it down, it makes sense to still be the same kind
of collection. So, +1 from me.

Nevin
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Re: [swift-evolution] [Review] SE-0174: Change `filter` to return an associated type

[Jaden Geller via swift-evolution]

I think that the alternatives considered section isn’t entirely correct. Even 
if we had a more expressive type system, it would not be possible to make the 
return value of `map` preserve the element type *while* still allowing types 
like `String`, which aren’t parameterized by an element, to conform.

I think this would require two separate mapping protocols (ignore the straw man 
names and syntax):

protocol Mappable: Sequence {
func map(_ transform: (Iterator.Element) -> Iterator.Element) -> Self
// could also add `mapInPlace`
}

protocol MappableFunctor: Mappable {
kind Self
func map(_ transform: (Iterator.Element) -> T) -> Self
}

I think we’d also require either a way for the generic function to conform to 
the non-generic signature if there exists a conforming instantiation if both 
functions were to have the same name.

Also, we’d probably want a way to say that the `T` in the generic signature has 
the same type constraints as the generic parameter would need to…

—

Anyway, the point is that we *could* consider adding the first protocol right 
now (or more likely, add the requirement to `Sequence`) even though the second 
protocol is not possible yet. Even if/when Swift’s type system can handle that, 
the first protocol will still be necessary for types like `String` that cannot 
conform to the second.

Cheers,
Jaden Geller
 
> On Apr 28, 2017, at 5:06 PM, Douglas Gregor via swift-evolution 
>  wrote:
> 
> Hello Swift community,
> 
> The review of SE-0174 "Change `filter` to return an associated type" begins 
> now and runs through May 3, 2017. The proposal is available here:
> 
> https://github.com/apple/swift-evolution/blob/master/proposals/0174-filter-range-replaceable.md
>  
> 
> Reviews are an important part of the Swift evolution process. All reviews 
> should be sent to the swift-evolution mailing list at
> 
> https://lists.swift.org/mailman/listinfo/swift-evolution 
> 
> or, if you would like to keep your feedback private, directly to the review 
> manager. When replying, please try to keep the proposal link at the top of 
> the message:
> 
> Proposal link:
> 
> https://github.com/apple/swift-evolution/blob/master/proposals/0174-filter-range-replaceable.md
>  
> 
> Reply text
> Other replies
>  What 
> goes into a review?
> 
> The goal of the review process is to improve the proposal under review 
> through constructive criticism and, eventually, determine the direction of 
> Swift. When writing your review, here are some questions you might want to 
> answer in your review:
> 
> What is your evaluation of the proposal?
> Is the problem being addressed significant enough to warrant a change to 
> Swift?
> Does this proposal fit well with the feel and direction of Swift?
> If you have used other languages or libraries with a similar feature, how do 
> you feel that this proposal compares to those?
> How much effort did you put into your review? A glance, a quick reading, or 
> an in-depth study?
> More information about the Swift evolution process is available at
> 
> https://github.com/apple/swift-evolution/blob/master/process.md 
> 
> Thank you,
> 
> -Doug Gregor
> 
> Review Manager
> 
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[swift-evolution] [Review] SE-0174: Change `filter` to return an associated type

[Douglas Gregor via swift-evolution]

Hello Swift community,

The review of SE-0174 "Change `filter` to return an associated type" begins now 
and runs through May 3, 2017. The proposal is available here:

https://github.com/apple/swift-evolution/blob/master/proposals/0174-filter-range-replaceable.md
Reviews are an important part of the Swift evolution process. All reviews 
should be sent to the swift-evolution mailing list at

https://lists.swift.org/mailman/listinfo/swift-evolution 

or, if you would like to keep your feedback private, directly to the review 
manager. When replying, please try to keep the proposal link at the top of the 
message:

Proposal link:

https://github.com/apple/swift-evolution/blob/master/proposals/0174-filter-range-replaceable.md
Reply text
Other replies
 What goes 
into a review?

The goal of the review process is to improve the proposal under review through 
constructive criticism and, eventually, determine the direction of Swift. When 
writing your review, here are some questions you might want to answer in your 
review:

What is your evaluation of the proposal?
Is the problem being addressed significant enough to warrant a change to Swift?
Does this proposal fit well with the feel and direction of Swift?
If you have used other languages or libraries with a similar feature, how do 
you feel that this proposal compares to those?
How much effort did you put into your review? A glance, a quick reading, or an 
in-depth study?
More information about the Swift evolution process is available at

https://github.com/apple/swift-evolution/blob/master/process.md 

Thank you,

-Doug Gregor

Review Manager
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